Cast Polymer Films Research Articles

Mesoscopic structures and dynamics of merocyanine J-aggregate studied by time-resolved fluorescence SNOM.

Time-resolved fluorescence SNOM is used to probe the mesoscopic structure and dynamics of long-chain merocyanine (C18MC) J-aggregates on glass plates prepared by spin coating, casting, and casting of water-soluble polymer films. A globular structure with an average diameter of approximately 1 microm and a height of approximately 50 nm was attributed to the J-aggregate of C18MC in the spin-coating film. In polymer films, the bandwidth of the absorption of J-aggregate is much narrower in polyvinyl alcohol (PVA, approximately 20 nm) than that in polyvinyl sulphate (PVS, approximately 60 nm). We have demonstrated that the large bandwidth of the spectrum is due to the inhomogeneous distribution of the J-aggregate. The fluorescence image of the J-aggregate in PVA film was rather uniform, whereas non-uniform distribution of the fluorescence was observed in PVS film. The fluorescence of C18MC J-aggregate in a small domain of PVA film was a single exponential decay with a lifetime as short as 19 ps, which was shorter than that in PVS film with a two-exponential decay (average lifetime of approximately 25 ps). The fluorescence lifetime of the J-aggregate and its single exponential behaviour are considered to be indicators of the uniform distribution of the J-aggregate. The non-uniform distribution of the J-aggregate in PVS film was interpreted in terms of electrostatic interaction between PVS and merocyanine.

Lithographically induced self-construction of polymer microstructures for resistless patterning

We have discovered and developed a method that can directly pattern polymer microstructures of arbitrary shapes without using a resist, exposure, chemical development, and etching. A mask with protruded patterns is placed a distance above an initially flat polymer film cast on a substrate. During a heating cycle that raises the temperature above the polymer’s glass transition temperature and then cooled back to the room temperature, we found that the polymer was attracted to the mask protrusions on their own, forming the mesas that have a lateral dimension identical to that of the mask protrusions, a height equal to the distance between the mask and the substrate, and a relatively steep sidewall. The method, termed lithographically induced self-construction, is important to the fabrication of polymer electronic and optoelectronic devices.

Drying kinetics of polymer films

AbstractDrying kinetics of a polymer film cast from a polymer–soluent solution is studied. A modelization of the whole drying process is performed, including the difision of soluent through the varnish layer, the moving interface, and the coupled heat and mass transfer between the interface and the drying air. The assumptions and the ualdity domain of the proposed modelization are thoroughly analyzed. In particular, comparison of the varnish temperature with its glass transition temperature all along the process allows us to determine the validity domain of the Fickian difision assumption. Because of the hypodifisiue behavior of polymer solutions, uery large concentration gradients appear in the layer, and the drying kinetics is characterized by two successive regimes. This two‐ stage kinetics is investigated first for typical conditions encountered in the packaging industry, where a film of a few microns is dried in a few seconds, thanks to hot air blown through nozzles. Then, different drying conditions corresponding to evaporation experiments at room temperature of thicker films of the same varnish are studied.

Solvent retention in solution-cast films of PMMA: study by dielectric spectroscopy

Conventional PMMA was dissolved in two different solvents (chloroform and toluene). Solid polymeric films were formed after casting of the solutions on a substrate (aluminium) and evaporation of the solvent at room temperature during several days. The dielectric properties of the solid films were studied by dielectric spectroscopy. The evolution of the loss tangent (tan δ) versus temperature was analysed. The results show that the tan δ peak, corresponding to the α-transition (glass transition), is shifted towards the lower temperatures, as compared with the bulk polymer obtained by heating press, without any solvent. The magnitude of the shift depends on the type of solvent. These results indicate that, in all cases, solvent molecules are retained and cannot be completely evaporated at room temperature, even after a long period. Solvent molecules are still trapped inside the PMMA films, but their effect on the polymer chains mobility differs in function of the nature of the solvent. Explanations based on acid–base interactions are proposed to try to understand this phenomenon. This work illustrates the interest of dielectric spectroscopy for studying in situ the properties of thin cast polymer films.

Studies of convective transport in evaporative casting of dense polymer films

Although several models have been developed to describe the evaporative casting of dense polymer films, none of them has included the convective transport terms which arise owing to the densification which occurs. In this paper we first describe a new finite element solution to the binary nonisothermal evaporative casting process which is used to confirm the predictions of the finite difference solution recently developed by Shojaie et al. (J. Mater. Process. Manu. Sci., 1 (1992) 181). This comparison then establishes that systematic deviations between experimental measurements and the model predictions of Shojaie et al. do not arise because of any inaccuracies in the numerical solution methodology. We then explore whether these deviations arise owing to omission of the convective transport terms by Shojaie et al. and all other modeling efforts. We employ a scaling analysis to demonstrate that convective transport effects can be significant in the evaporative casting process. The convective transport terms then are incorporated into the nonisothermal evaporative casting model of Shojaie et al. for the cellulose acetate/acetone system. The model predictions both with and without convective transport are compared to real-time gravimetric and surface-temperature data. This study indicates that ignoring convective transport can result in differences as large as 40% in the model predictions. The model predictions incorporating convective transport are in quantitative agreement with real-time data at short evaporation times, but progressively deviate at longer times. This deviation is thought to be due to the use of an equilibrium equation-of-state for the solution density as a function of concentration.

Poly(L-Lactic Acid-Co-Aspartic Acid): Interactive Polymers for Tissue Engineering

AbstractOne of the challenges in the field of tissue engineering is the development of optimal materials for use as scaffolds to support cell growth and tissue development. For this purpose, we are developing synthetic, biodegradable polymers with functional sites that provide the opportunity to covalently attach biologically active molecules to the polymers, so they can predictably interact with cells in a favorable manner to enhance cell attachment and growth. The preparation of poly(L-lactic acid-co-aspartic acid) comb-like graft copolymers from poly(L-lactic acid-co-β-benzyl-L-aspartate), and the casting of polymer films by solvent evaporation were carried out.

Synthesis, characterization, and properties of colorless rigid‐rod poly(benzobisthiazole) derived from bicyclo[2.2.2]octane

AbstractPolycondensation in polyphosphoric acid of 2,5‐diamino‐1,4‐benzene dithiol dihydrochloride with bicyclo[2.2.2]octane‐1,4‐dicarboxylic acid, as well as the corresponding dimethyl ester or diacid chloride, led to rigid‐rod benzobisthiazole polymers. Colorless and soluble polymers with intrinsic viscosities as high as 30.6 dL/g (methanesulfonic acid, 30°C) were obtained. The ultraviolet‐visible spectrum of a polymer film cast from methanesulfonic acid under reduced pressure displayed no absorptions in the visible range (400–900 °m). The polymer was thermooxidatively stable up to 420°C in air as determined by thermogravimetric analysis. Fibers spun from a lyotropic polyphosphoric acid solution exhibited a tensile strength of 300–450 Ksi, a modulus of 26 Msi, and a compressive strength of 53 Ksi. Wide‐angle X‐ray scattering patterns of polymer fibers indicated a 3‐dimensional crystal structure rather than a nematic liquid crystal structure. © 1994 John Wiley & Sons, Inc.

Dehydration of Isopropanol by Pervaporation Using Aromatic Polyetherimide Membranes

Abstract Aromatic polyetherimide membranes were prepared by the phase inversion method and tested for the pervaporation separation of water from isopropanol with emphasis on the breaking of azeotropic composition and the dehydration of high concentrations of isopropanol. It was found that the membrane selectivity was enhanced by partial evaporation of the solvent in the cast polymer films prior to the gelation step during membrane formation. The membrane performance was shown to be dependent on the feed concentration and the operating temperature. At a feed temperature of 25°C and a permeate pressure of 133 Pa, separation factors of 173 and 384 were achieved for the dehydration of isopropanol solutions at 0.68 (azeotropic composition) and 0.96 mole fractions isopropanol, respectively, with reasonably high permeation rates. The utility of the membranes for the proposed separation was demonstrated; however, these membranes were not prepared under optimized conditions and thus a continuous study is required ...

Two-dimensional undulation pattern on free surface of polymer film cast from solution

Non-linear pattern formation in polymer systems has been studied. We present the undulation pattern observed on the free surface of a polymer film cast from solution, for poly(styrene- ran-butadiene) random copolymer and for mixtures of polystyrene and dioctylphthalate. The undulation pattern was similar to a hexagonal cellular pattern observed for low viscous fluid produced by Rayleigh-Bénard convection. It was considered that steady-state convective flows occur in a polymer solution with relatively low viscosity, which is induced by solvent evaporation in the earlier stage of casting. Inhomogeneity of the polymer concentration attributed to the convection was considered to play an important role in the pattern formation.

Highly organized macroscopic pattern observed on the free surface of a polymer film cast from a solution

A highlly organized macroscopic pattern observed on the free surface of a poly(styrene-b-butadiene-b-styrene) triblock copolymer film cast from its tomluene solution is presented. The undulation pattern of the free surface is explainedin terms of hydrodynamic instability

Chemical synthesis of processible electrically conducting poly(3‐dodecylthiophene)

AbstractThe chemical synthesis of poly(3‐dodecylthiophene) is reported. The polymer was characterized by 1H‐NMR, IR and UV absorption spectroscopic techniques. The room temperature electron spin resonance spectrum yielded a g value of 2.0091 and a linewidth of 6.60 Gauss. The solution cast polymer films after doping with iodine exhibited an electrical conductivity of 12 S/cm.

Waveguide CARS spectra of 4,4'-dibromobiphenyl dispersed in a polymethylmethacrylate optical waveguide

With the use of a waveguide geometry, CARS spectroscopy is found to be an extremely sensitive technique to detect a very low concentration of molecules dispersed in a matrix. Using a planar optical waveguide geometry, the CARS spectra of 4,4'-dibromobiphenyl dispersed in a ≈3 μm thick polymethylmethacrylate polymer film cast on a quartz substrate has been recorded using picosecond optical pulses. Different vibrational bands have been recorded using the TE 0 waveguide mode for both the pump and the probe pulses.

New polyurethanes with conjugated triple bonds

Urethane polymers possessing two conjugated -C≡C- triple bonds per repeating unit are synthesized. Polyurethanes are characterized by their infrared absorption spectra, UV abrsorption spectra and elementel analysis. Their molecular weights and limit intrinsic viscosities are determined. Solutions of these polymers in various solvents do not show any reactivity when exposed to light or heat. However the solid polyurethanes and solvent cast polyurethane films obtained from trimethyl hexamethylene diisocyanate, and isophoron diisocyanate quite rapidly develop red-brown colour on annealing at elevated temperatures, below their melting point. During this process the polymers themselves and solvent cast polymer films become insoluble in any of the solvents. Their IR and UV absorption spectra before and after annealing are examined and the band gaps are calculated from the spectral data.

Electrochemical, electrochromic, and conductive properties of poly(N-alkyldiphenylamine) polymers

Chemically prepared poly(N-alkyldiphenylamine) polymers are conductive and electrochemically reversibly dopable in organic and aqueous solutions; cast polymer films exhibit multiple, reversible colour changes in 1 M LiCLO4 in acetonitrile or 1 M HClO4 aqueous under potential cycling between 0.0 and 1.0 vs. Ag/AgCl or when dipped in aqueous solutions having different pH.

Viscoelastic and statistical thermodynamic approach to the study of the structure of polymer film casting solutions for making RO/UF membranes

Taille des aggregats supermoleculaires de copolymeres isophenylene et terephtalamide utilises pour faire des membranes d'ultrafiltration (UF) pour osmose inverse (RO)

Photoinduced electron transfer quenching of rhodamine B in polymer films

Photoinduced electron transfer reactions of rhodamine B with several redox quenchers in solution-cast films of poly( N-vinylpyrrolidone) have been investigated using fluorescence spectroscopy. The quenching of the rhodamine B fluorescence has been used to examine the efficiency of photo-induced electron transfer in a rigid amorphous polymer matrix. The data obtained show that the electron transfer efficiency is a function of the free energy of the transfer and depends on the redox potential of the quencher. The data are analyzed using theories of electron transfer in solid media and are correlated with the redox potentials of the quenchers to derive the distance dependence of the excited state transfer. Photoinduced electron transfer between rhodamine B and both donor and acceptor quenchers in the cast polymer films is observed to occur at distances of up to about 15 Å for this system.

Diffusive desorption of small solute molecules from amorphous polymers: poly(methyl methacrylate), poly (vinyl acetate) and poly( n-alkyl 2-cyanoacrylates)

Diffusion coefficients of some aromatic substances in poly(vinyl acetate) and poly(methyl methacrylate) have been measured from desorption rates into aqueous buffers from solid solutions of diffusant in cast polymer films. With ordinary spectrophotometric instrumentation, extension of the measurable range of the diffusion coefficient at infinite dilution to below 10 −21 m 2 sec −1 is sometimes possible. Measures values below 10 −12 m 2 sec −1 are generally much more quickly obtained, and are apparently at least as reproducible as those obtained by time-lag methods, permitting differential effects of diffusant molecular weight and shape to be studied, with solutes of higher molecular weight than those to which previous published studies were confined. Diffusion coefficients of the same solutes in a number of poly( n-alkyl 2-cyanoacrylates) were measured by desorption from polymer particles and films. The rank order and general dependence of diffusivity upon molecular weight and shape is similar in all three polymers. There is a tendency for the ionic and basic solutes to become bound, probably by covalent linkage, to poly( n-alkyl 2-cyanoacrylate) molecular chain ends.

Pyroelectric polymer films

The objective of this investigation was to synthesize polymeric materials of high pyroelectric efficiency and to prepare thin test films suitable for use in pyroelectric vidicons. In our investigation of vinyl-addition polymers with highly polar pendant groups, we concentrated on atactic and isotactic substituted styrenes. Five atactic 4-substituted styrenes, poly(4-bromostyrene), poly(4-nitrostyrene), poly-(4-chlorostyrene), poly(4-methoxystyrene) and poly(4-fluorostyrene), were synthesized and evaluated, as were four isotactic 4-substituted styrenes, poly(4-bromostyrene), poly(4-chlorostyrene), poly(4-methoxystyrene) and poly(4-fluorostyrene). Hot-pressing was found to be a successful method of fabricating thick films of those polymers which did not undergo thermal decomposition near the melting point. Solvent casting of polymer films directly onto the test substrate proved to be the only practical method of handling brittle thin polymer films. Film formation by stretching and blowing was not found to be suitable for most of the polymers investigated. Laser evaporation was found to be a very useful technique for the preparation of polymer test films. Laser-evaporated poly(vinyl fluoride) showed the highest known pyroelectric coefficient for this material (1.8×10 -9C/cm 2 °K). None of the poly(4-substituted styrenes) showed any substantial pyro-electric behavior. This result can be attributed to their characteristics helical structure and lack of net permanent dipole moment.

Reaction of Nitrogen Dioxide with Nylon 66

Chain scission of nylon 66 films due to exposure to nitrogen dioxide at a pressure of 0.5 mmHg has been studied as a function of temperature, film thickness, and polymer morphology. The rate of random chain scission in cast polymer films is very sensitive to changes in morphology caused by small variations in solvent composition for film casting and in mode of preparation. Decrease of chain scission with film thickness indicates that diffusion of NO2 into the polymer is rate-determining. The magnitude of the energy of activation is in agreement with this finding. It is assumed that amide links in the chain folds of polymer molecules located in the interfacial region between amorphous and crystalline polymer portions are especially susceptible to chain scission, due to their strain energy.

Spin casting of polymer films

AbstractA versatile technique for spin casting of small polymer films within a cylindrical open faced mold is described. The high centripetal acceleration, about 500g, provides outstanding thickness uniformity and freedom from interior defects. The casting apparatus may be provided with pressure, temperature, and atmosphere control. A compact unit for simultaneous casting of four films is illustrated.